Passive detectors for imaging systems

ABSTRACT

Passive detector structures for imaging systems are provided which implement unpowered, passive front-end detector structures with direct-to-digital measurement data output for detecting incident photonic radiation in various portions (e.g., thermal (IR), near IR, UV and visible light) of the electromagnetic spectrum.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Continuation of U.S. patent application Ser. No.15/383,779, filed on Dec. 19, 2016, now U.S. Pat. No. 10,247,614, whichis a Continuation of U.S. patent application Ser. No. 14/677,954, filedon Apr. 2, 2015, now U.S. Pat. No. 9,523,612, which is a Continuation ofU.S. patent application Ser. No. 13/588,441, filed on Aug. 17, 2012, nowU.S. Pat. No. 9,012,845, which claims priority to U.S. ProvisionalPatent Application Ser. No. 61/524,669, filed on Aug. 17, 2011, thedisclosures of which are incorporated herein by reference.

TECHNICAL FIELD

The field generally relates to detector structures for imaging systemsand, in particular, to passive front-end detector structures withdirect-to-digital measurement data output for detecting incidentphotonic radiation in various portions (e.g., thermal (IR), near IR, UVand visible light) of the electromagnetic spectrum.

BACKGROUND

In general, MEMS technology has been utilized to construct infraredlight detectors. One such light (IR photonic) detector includes a MEMSstructure with a capacitor and a cantilever arm. The capacitor has afixed plate and a mobile plate. The cantilever arm has a first end,which is fixed to a substrate, and a second end, which is fixed to themobile capacitor plate. The cantilever arm also includes a bimorphportion that bends in response to being heated by absorption of infraredlight. Bending of the bimorph portion displaces the mobile plate in amanner that changes the distance between the mobile and fixed plates ofthe absorber. Thus, illumination of the MEMS structure by infrared lightproduces a measurable change in an electrical property of the structure,i.e., the capacitance of the capacitor. By measuring variations in suchcapacitances, the light detector is able to determine the intensity ofinfrared light illuminating each MEMS structure, i.e., each pixelelement of the detector.

Another common type of thermal radiation detector is the un-cooledmicro-bolometer. In general, a micro-bolometer comprises a thin filmabsorbing detector and a thermal isolation structure. Incident radiationabsorbed by the detector induces a temperature increase that furtherresult in variations of the electric conductivity of the thin filmdetector. The electrical conductivity is used to determine the intensityof the incident radiation.

The principal limitations of detectors including cantilever andmicro-bolometer type structures arises from the electrical connectionsrequired to read the temperature variations or changes in electricalcharacteristics (e.g., resistance, capacitance) induced by incidentradiation. Moreover, the complexity of manufacturing pixelinterconnections and the readout circuitry has maintained themanufacturing costs of the detector structures prohibitive for manyapplications. Furthermore, these electrical interconnections impair thethermal isolation between the pixels and the readout system and, as aresult, limit the thermal sensitivity of the detector. Semiconductor andquantum electronic detector methodologies are very prone toself-generated and external noise sources that lower the systemssensitivity and require complex and expensive methods to mitigate theproblems.

SUMMARY

Exemplary embodiments of the invention include passive detectorstructures for imaging systems and, in particular, to unpowered, passivefront-end detector structures with direct-to-digital measurement dataoutput for detecting incident photonic radiation in various portions(e.g., thermal (IR), near IR, UV and visible light) of theelectromagnetic spectrum.

For example, in one exemplary embodiment of the invention, a photondetector device includes a substrate, a resonator member, a passivedetector structure, and a digital circuit. The resonator member isdisposed on the substrate and outputs a signal having an oscillatingfrequency. The passive detector structure is disposed on the substrateand is mechanically coupled to the resonator member. The passivedetector structure includes a detector member that is mechanicallydistorted in response to photon exposure to apply a mechanical force tothe resonator member and change the oscillating frequency of theresonator member in response to the mechanical force. In someembodiments, the detector member is formed of one or more materialshaving a thermal coefficient of expansion that causes the detectormember to become mechanically distorted by thermal expansion andcontraction. The digital circuit is coupled to the resonator member. Thedigital circuit operates by, e.g., determining the oscillating frequencyof the resonator member, which changes due to the mechanical forceexerted on the resonator member by the passive detector structure, anddetermining an amount of incident photonic energy absorbed by thedetector member based on the determined oscillating frequency of theresonator member.

In another exemplary embodiment, a method for detecting photonic energyincludes exposing a passive detector member to incident photonic energyto cause the detector member to be mechanically distorted in response tophoton exposure, applying a mechanical force to a resonator member inresponse to mechanical distortion of the passive detector member,determining an oscillating frequency of the resonator member, whichchanges due to the mechanical force exerted on the resonator member bythe passive detector member, and determining an amount of incidentphotonic energy absorbed by the detector member based on the determinedoscillating frequency of the resonator member. In other embodiments, themethod further includes generating image data using the determinedoscillating frequency. The amount of incident photonic energy absorbedby said detector member may be determined by generating count data bycounting a number of digital pulses in an output signal of the resonatormember for a given counting period, and determining a level of photonicexposure of the detector member based on the count data.

These and other exemplary embodiments of the present invention willbecome apparent from the following detailed description of illustrativeembodiments thereof, which is to be read in connection with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a photon detector according to anexemplary embodiment of the invention, which is based on a coefficientof thermal expansion (CTE) framework.

FIG. 2 is a top view of a photon detector according to another exemplaryembodiment of the invention, which is based on a CTE framework.

FIG. 3 is a top view of a photon detector according to another exemplaryembodiment of the invention, which is based on a CTE framework.

FIG. 4 is a top view of a photon detector according to another exemplaryembodiment of the invention, which is based on a CTE framework.

FIG. 5 is a perspective view of a photon detector according to anotherexemplary embodiment of the invention, which is based on a CTEframework.

FIGS. 6A and 6B illustrate a photon detector according to anotherexemplary embodiment of the invention, which is based on a CTEframework, wherein FIG. 6A is a top perspective view of the photondetector and wherein FIG. 6B is a side view of the photon detector takenalong line 6B-6B in FIG. 6A.

FIG. 7 is a perspective view of a visible light detector according to anexemplary embodiment of the invention, which is based on aphoton-induced coefficient of expansion (PICE) concept.

FIG. 8 is a perspective view of a detector according to anotherexemplary embodiment of the invention, which is based on a voltageinduced distortion (VID) framework.

FIG. 9 is a side view of a detector according to another exemplaryembodiment of the invention, which is based on a VID framework.

FIG. 10 is a side view of a detector according to another exemplaryembodiment of the invention, which is based on a VID framework.

FIG. 11 is a side view of a detector according to another exemplaryembodiment of the invention, which is based on a VID framework.

FIG. 12 is a side view of a detector according to another exemplaryembodiment of the invention, which is based on a VID framework.

FIG. 13 schematically illustrates a top view and a side view of abellows-shaped detector member, according to an exemplary embodiment ofthe invention.

FIG. 14 schematically illustrates a top view and a side view of abellows-shaped detector member that is formed of alternating materialsthat are different.

FIGS. 15A and 15B illustrate a photon detector according to anotherexemplary embodiment of the invention, which is based on a CTEframework, wherein FIG. 15A is a top view of the photon detector andwherein FIG. 15B is a cross-sectional view of the photon detector takenalong line 15B-15B in FIG. 15A.

FIGS. 16A and 16B illustrate a photon detector according to anotherexemplary embodiment of the invention, which is based on a CTEframework, wherein FIG. 16A is a cross-sectional view of the photondetector taken along line 16A-16A in FIG. 16B, and wherein FIG. 16B is atop view of the photon detector.

FIGS. 17A and 17B illustrate a photon detector according to anotherexemplary embodiment of the invention, which is based on a CTEframework, wherein FIG. 17A is a cross-sectional view of the photondetector taken along line 17A-17A in FIG. 17B, and wherein FIG. 17B is atop view of the photon detector taken along line 17B-17B in FIG. 17A.

FIG. 18 graphically illustrates an advantage of using adirect-to-digital passive detector framework over conventional analogsignal detector or quantum electronic designs, according to exemplaryembodiments of the invention.

FIG. 19 is a block diagram of an imager system based on passivedetectors, according to an exemplary embodiment of the invention.

FIG. 20 is a block diagram that illustrates another exemplary embodimentof a pixel unit and pixel circuitry, which can be implemented in theimager system of FIG. 19.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

Exemplary embodiments of the invention will now be described in furtherdetail below with regard to passive detector structures for imagingsystems and, in particular, to unpowered, passive front-end detectorstructures with direct-to-digital measurement data output for detectingincident photonic radiation in various portions (e.g., thermal (IR),near IR, UV and visible light) of the electromagnetic spectrum.Exemplary passive detector frameworks described herein provide a newparadigm for detecting incident photonic energy in the electromagneticspectrum (e.g. infrared, visible, and ultraviolet spectrums), as well aselectromagnetic radiation in the microwave, teraherz and x-ray portionsof the electromagnetic spectrum. The passive detector frameworksimplement a direct-to-digital measurement with no analog front end orquantum semiconductors, thereby providing a low noise, low power, lowcost and ease of manufacture detector design, as compared toconventional CMOS or CCD detector devices. The exemplary passivedetector frameworks with direct-to-digital measurement data output asdescribed herein do not use any quantum photonic or electron conversiontechniques, and have none of the technological, manufacturing or noiseproblems associated with conventional imager technologies as discussedabove.

As discussed in further detail below, exemplary embodiments of theinvention are based on various passive detector methodologies to detectvarious wavelengths of UV, visible, near IR, Mid IR and Far IR andTerahertz radiation. The exemplary passive detector paradigms describedherein include CTE (coefficient of thermal expansion), PICE (photoninduced coefficient of expansion), and VID (voltage induced distortion)detector frameworks. In general, these detector frameworks implement apassive detector structure comprising a detector member that ismechanically distorted in response to photon or electromagneticradiation exposure to apply a mechanical force to a resonator member andchange the oscillating frequency of the resonator member in response tothe mechanical force. A digital circuit is coupled to the resonatormember and operates to determine the oscillating frequency of theresonator member, which changes due to the mechanical force exerted onthe resonator member by the passive detector structure, and to determinean amount of incident photonic energy or electromagnetic radiationexposure of the detector member based on the determined oscillatingfrequency of the resonator member.

With a CTE framework, a passive detector member (e.g., ribbon(s) orplate(s)) is made of one or more materials having a thermal coefficientof expansion, wherein the detector member expands and contracts inresponse to incident photonic energy to exert a mechanical force on aresonator member and vary the oscillating frequency of the resonatormember.

With a PICE framework, a passive detector member is made of one or morematerials that change their shape and size when exposed to specificwavelengths of electromagnetic radiation. The detector member ismechanically deformed (e.g., expands and contracts) in response toexposure of incident electromagnetic radiation to exert a mechanicalforce on a resonator member and vary the oscillating frequency of theresonator member.

With a VID framework, for wavelengths such as X-rays (1 nm) through NearIR (30, a detector member can be formed of one or more materials, whichgenerates a voltage in response to exposure of incident radiation. Thegenerated voltage is applied to resonator member (e.g., a piezo materiallayer), causing the resonator member to mechanically distort and changethe oscillating frequency of the resonator member. For example, avoltage can be generated from photonic exposure of a detector memberformed of a photovoltaic (PV) material. In addition, for thermal IRwavelengths (3 to 14μ), a detector member can be formed of apyroelectric material to generate a voltage that can be applied todistort a piezo resonator member and change the oscillating frequency ofthe resonator member.

FIGS. 1-6 are perspective views of various passive detector frameworksaccording to exemplary embodiments of the invention, which are based ona CTE framework. For example, FIG. 1 is a perspective view of a photondetector according to an exemplary embodiment of the invention. Ingeneral, the photon detector (100) comprises a substrate (102), digitallogic circuitry (104), a parabolic mirror (106), and a bridge structureformed on the substrate (102). The bridge structure includes a firstsupport member (110), a second support member (120) and a detectormember (130) suspended between the support members (110) and (120) abovethe substrate (102). The second support member (120) is a resonatormember that operates at a resonant frequency and the first supportmember (110) is a fixed insulating support structure. The detectormember (130) (or ribbon) comprises a bi-metal ribbon (132) having athermal coefficient of expansion, which expands and contracts byabsorption of incident infrared energy to exert force on the resonatormember (120), and a photon energy absorbing layer (134). An insulatingmaterial layer (122) is disposed between the end of the ribbon (130) andthe resonator member (120) to provide thermal isolation between theribbon (130) and the resonator support structure (120). The digitallogic circuit (104) is coupled to the resonator member (120) fordetermining a change in oscillating frequency of the resonator member(120) due to force exerted on the resonator member (120) by the thermalexpansion and contraction of the ribbon structure (130), wherein thechange in frequency is correlated to an amount of incident infraredenergy absorbed by the ribbon structure (130).

More specifically, the ribbon (130) is made of materials that aresensitive to IR heat causing the ribbon (130) to expand and contractbased on the absolute amount of incident IR photons striking the ribbon(130). The metallic materials forming the bi-metal ribbon layer (132)may be formed with any suitable materials having a negative and/orpositive coefficient of thermal expansion. The photon energy absorbinglayer (134) may be formed of any suitable material (such as carbon, SiC,etc.) having a peak sensitivity at any desired IR wavelength in the IRspectrum from 1 micron to 30 microns. In other exemplary embodiments,filter materials can be deposited on top of the photon energy absorbinglayer (134) to make the sensitivity narrower. A narrow response may beachieved by doping the photon energy absorbing material layer (134) withspectral material that either reflects or negates the response inundesirable portions of the IR spectrum.

As shown in FIG. 1, the ribbon (130) is suspended like a bridge betweenthe supports (110) and (120) leaving the area under the ribbon (130)open, unsupported and not in contact with any parts of the rest of thepixel structure. Only the end portions of the ribbon (130) are attachedto any portion of the pixel structure (100). This design allows theribbon (130) to have the least possible mass such that with a low mass,the ribbon (130) can heat soak from the incident IR photon exposure inthe shortest amount of time. This will make the sensor react as fast aspossible. A fast reaction time will allow faster imaging. The parabolicreflector (106) can be placed under the ribbon (130) on the substrate(102) to increase the pixels fill-factor allowing more IR photons tostrike and affect the ribbon from the top and bottom. Fill-factor is thetotal amount of surface area of the pixel that is capable of collectingthe incoming incident photons. The pixel has a finite dimension andfinite area. The higher the percentage of fill-factor the more of thepixels area is used to collect photons. The higher the fill-factorpercentage, the better the pixels sensitivity, and performance. Themirror 106 can be parabolic, flat or V shaped, or may not be implementedat all.

FIG. 2 is a perspective view of a photon detector according to anotherexemplary embodiment of the invention. In general, FIG. 2 depicts aphoton detector (200) that comprises a substrate (102), digital logiccircuitry (104), a parabolic mirror (106), and a bridge structure formedon the substrate (102). The bridge structure includes a first supportmember (210), a second support member (220) and two ribbon members (230)and (240) suspended between the support members (210) and (220) abovethe substrate (102). The first ribbon (230) comprises a bi-metal layer(232) and a photon energy absorbing layer (234) and the second ribbon(240) comprises a bi-metal layer (242) and a photon energy absorbinglayer (244). The second support member (220) is a resonator member thatoperates at a resonant frequency and the first support member (210) is afixed insulating support structure. An insulating layer (222) isdisposed between the ribbon structures (230) and (240) and the resonatorsupport structure (220) to provide thermal isolation.

The thermal detector (200) is similar to the detector (100) of FIG. 1,except for the inclusion of two ribbon members (230) and (240) whichprovided added functionality. In particular, in one exemplaryembodiment, each ribbon (230) and (240) can be designed with differentmaterials to detect IR radiation with sensitivity at two differentportions of the IR spectrum (e.g., 10 microns and 4 microns), so thatthe detector (200) can provide enhanced sensitivity at more than onewavelength. In another exemplary embodiment, each ribbon (230) and (240)can be designed with similar materials to detect IR radiation withsensitivity in one portion of the IR spectrum but with a widerbandwidth, enabling the linearity of the detector response to becontrolled and tailored over a given thermal range of pixel designspecifications and parameters.

FIG. 3 is a perspective view of a photon detector according to anotherexemplary embodiment of the invention. In general, FIG. 3 depicts aphoton detector (300) that comprises a substrate (102), digital logiccircuitry (104), a parabolic mirror (106), and a bridge structure formedon the substrate (102). The bridge structure includes a first supportmember (310), a second support member (320) and a plurality of ribbonmembers (330), each ribbon (330) including a bimetal layer (332) and aphoton energy absorbing layer (334). The second support member (320) isa resonator member that operates at a resonant frequency and the firstsupport member (310) is a fixed insulating support structure. Aninsulating layer (322) is disposed between the ribbon structures (330))and the resonator support structure (320) to provide thermal isolation.

The thermal detector (300) is similar in operation to the detector (100)discussed above with reference to FIG. 1, for example, except for theinclusion of multiple smaller ribbon structures (330) each similarlydesigned to operate at a given portion of the IR spectrum. However, theuse of multiple ribbons (330) allows each ribbon to have lower mass, ascompared to the single ribbon structure of FIG. 1. With lower mass pereach individual ribbon (330), each of the ribbons (330) can react tothermal energy (expand and contract) faster, thereby reducing theresponse time of the pixel.

FIG. 4 is a perspective view of a photon detector according to anotherexemplary embodiment of the invention. In general, FIG. 4 depicts aphoton detector (400) that comprises a substrate (102), digital logiccircuitry (104), a parabolic mirror (106), and a dual bridge structureformed on the substrate (102). The dual bridge structure includes afirst support member (410), a first resonator support member (420), asecond resonator support member (424), a first ribbon member (430)connected between the first support member (410) and the first resonatorsupport member (420), and a second ribbon member (440) connected betweenthe first support member (410) and the second resonator support member(424). Each ribbon (430) and (440) includes a respective bimetal layer(432) and (442) and a respective photon energy absorbing layer (434) and(444). Insulating layers (422) and (426) are disposed between therespective ends of ribbon structures (430) and (440), and respectiveresonator support members (420) and (424).

The thermal detector (400) is similar in operation and design to thedetectors (100) and (200) discussed above, for example, except that thedetector can operate in two different spectrums independent of eachother. This is made possible by use of the separate ribbon structures(430) and (440) and independent resonator support members (420) and(424). In particular, each ribbon (430) and (440) can be designed withdifferent materials to detect IR radiation with sensitivity at twodifferent portions of the IR spectrum (e.g., 10 microns and 4 microns)so the control logic circuitry (104) can be operated to detect IR energyin one or both of the supported spectrums at a given time.

FIG. 5 is a perspective view of a photon detector according to anotherexemplary embodiment of the invention. In general, FIG. 5 depicts aphoton detector (500) that comprises a substrate (102), digital logiccircuitry (104), a first and second parabolic mirror (106) and (108),and a bridge structure formed on the substrate (102). The bridgestructure includes a first support member (510), a first resonatorsupport member (520), a second resonator support member (524), a firstribbon member (530) connected between the first support member (510) andthe first resonator support member (520), and a second ribbon member(540) connected between the first support member (510) and the secondresonator support member (424). Each ribbon (530) and (540) includes arespective bimetal layer (532) and (542) and a respective photon energyabsorbing layer (534) and (544). Insulating layers (522) and (526) aredisposed between the respective ends of ribbon structures (530) and(540), and respective resonator support members (520) and (524).

The thermal detector (500) is similar in operation and design to thedetectors (100) discussed above, for example, except that in theframework of FIG. 5, a pair of adjacent pixels are designed to share asingle insulating support member (510), as compared to FIG. 1, whereineach pixel includes a separate insulating support member. The frameworkof FIG. 5 provides a more compact design, which can also be implementedwith the detector frameworks depicted in FIGS. 2-4.

FIGS. 6A and 6B illustrate a photon detector according to anotherexemplary embodiment of the invention. In general, FIG. 6A is aschematic top perspective view of a photon detector (600) and FIG. 6B isa schematic side view of the photon detector (600) taken along line6B-6B in FIG. 6A. Referring to FIGS. 6A and 6B, the photon detector(600) comprises a substrate (102), digital logic circuitry (104), aparabolic mirror (106), a bridge structure formed on the substrate(102). The bridge structure includes a first support member (610), asecond support member (612), a third support member (614), a resonatormember (620), an insulating layer (622), and a ribbon member (630). Theresonator member (620) is connected between the second and third supportmembers (612) and (614), wherein the resonator member (620) is suspendedabove the substrate (102) (which is in contrast to previously discussedembodiments in which the resonator member serves as a support memberanchored to the substrate).

The ribbon structure (630) comprise a bimetal layer (632) and a photonenergy absorbing layer (634) (e.g., carbon, carbon nanotubes, SiC,etc.). The ribbon structure (630) is connected between the first supportmember (610) and the resonator member (620). In particular, the ribbonstructure (630) comprises a plurality of tabs (632A, 632B, 632C and632D) which are integrally formed as part of the bimetal layer (632),wherein the ribbon (630) is connected to the resonator member (620) viathe tabs (632A, 632B, 632C and 632D). The use of the tabs (632A, 632B,632C and 632D) and the insulating layer (622) serve to thermally isolatethe resonator member (620) from the bimetal layer (632). In theexemplary embodiment of FIGS. 6A and 6B, the second support member (612)provides supply voltage V+ to the resonator member (620) and the thirdsupport member (614) provides a ground connection for the resonatormember (620).

With PICE-based pixel frameworks, materials are used that will distorttheir shape when exposed to specific wavelengths between X-rays (1 nm)through Near IR (3μ). For example, a CdS structure will change shapewhen exposed to visible light. FIG. 7 is a perspective view of a visiblelight detector (700) framework according to an exemplary embodiment ofthe invention, which is based on the PICE concept. In general, thedetector (700) comprises a substrate (102), digital logic circuitry(104), and a bridge structure formed on the substrate (102). The bridgestructure includes a first support member (710), a second support member(720) and a ribbon member (730) suspended between the support members(710) and (720) above the substrate (102).

The support member (720) is a resonator member that operates at aresonant frequency and the second support member (710) is a fixedinsulating support structure. The ribbon structure (730) is made from aphoto-sensitive material (such as CdS, ZnO) having a photon inducedcoefficient of expansion, which causes mechanical deformation of theribbon structure (7300 caused directly by photonic exposure. Aninsulating material layer (722) is disposed between the end of theribbon (730) and the resonator member (720) to provide thermal andelectrical isolation between the ribbon (730) and the resonator supportstructure (720).

The ribbon structure (730) includes a layer of material (e.g., CdS)which receives incident photons, causing the ribbon (730) to stress andchange length. This stress is transferred to the resonator (720), whichcauses it to change its resonant frequency in proportion to the amountof incident photon exposure. The digital logic circuit (104) is coupledto the resonator member (720) for determining a change in oscillatingfrequency of the resonator member (720) due to force exerted on theresonator member (720) by the mechanical expansion and contraction ofthe ribbon structure (730), wherein the change in frequency iscorrelated to an amount of incident photon energy received by the ribbonstructure (730).

FIGS. 8-14 are perspective views of various detector frameworksaccording to exemplary embodiments of the invention, which are based onthe VID concept. These frameworks provide a passive detectorarchitecture for wavelengths, X-rays (1 nm) through Near IR (3μ),wherein a ribbon material produces a voltage from photon exposure, andwherein the voltage is applied to a piezo material layer that will causethe material to distort and create the stress to alter the resonatorfrequency. In other embodiments, for thermal IR wavelengths, apyroelectric material may be used to generate a voltage that whenapplied to a piezo material layer will cause the material to distort andcreate the stress to alter the resonator frequency.

In particular, FIG. 8 is a perspective view of a visible/UV lightdetector (800) framework according to an exemplary embodiment of theinvention, which is based on the VID concept. In general, the detector(800) comprises a substrate and digital logic circuitry (notspecifically shown, but similar to all embodiments discussed above) anda bridge structure formed on the substrate 102. The bridge structureincludes a first support member (810), a second support member (820) anda ribbon structure (830) suspended between the support members (810) and(820) above the substrate.

The support member (820) is a resonator member that operates at aresonant frequency and the support member (810) is a fixed insulatingsupport structure. The ribbon structure (830) comprises photon sensitivelayer (832), an insulating layer (834), a piezoelectric layer (836) andconnecting members (838) that provide electrical connections betweenlayers (832) and (836). The photon sensitive layer (832) is made from aphoto-sensitive material that generates a voltage from exposure toincident photons (visible light or UV radiation). The voltage generatedby layer (8320 is transferred to the piezoelectric layer (836) viaconnections (838), wherein the piezoelectric layer (836) reacts to thevoltage by creating stress as it tries to change its length. This stressis transferred to the resonator (820), which causes it to change itsresonant frequency in proportion to the amount of incident photonexposure. The digital logic circuit coupled to the resonator member(820) determines a change in frequency of the resonant frequency of theresonator member (820) due to force exerted on the resonator member(820) by the mechanical expansion and contraction of the piezo layer(836), wherein the change in frequency is correlated to an amount ofincident photon energy received by the ribbon structure (830). Thisframework operates on a photovoltaic effect.

FIG. 9 is a perspective view of a detector (900) framework according toanother exemplary embodiment of the invention, which is based on the VIDconcept. In general, the detector (900) comprises a substrate anddigital logic circuitry (not specifically shown, but similar to allembodiments discussed above) and a bridge structure formed on thesubstrate. The bridge structure includes a first support member (910), asecond support member (920) and a ribbon structure (930) suspendedbetween the support members (910) and (920) above the substrate.

The support member (920) is a resonator member that operates at aresonant frequency and the support member (910) is a fixed insulatingsupport structure. The ribbon structure (930) comprises an IR sensitivelayer (932), an insulating layer (934), a piezoelectric layer (936) andconnecting members (938) that provide electrical connections betweenlayers (932) and (936). The IR sensitive layer (932) is made from apyroelectric material that generates a voltage from exposure to incidentIR radiation. The voltage generated by layer (932) is transferred to thepiezoelectric layer (936) via connections (938), wherein thepiezoelectric layer (936) reacts to the voltage by creating stress as ittries to change its length. This stress is transferred to the resonator(920), which causes it to change its resonant frequency in proportion tothe amount of incident IR exposure. The digital logic circuit coupled tothe resonator member (920) determines a change in the oscillatingfrequency of the resonator member (920) due to force exerted on theresonator member (920) by the mechanical expansion and contraction ofthe piezo layer (936), wherein the change in frequency is correlated toan amount of incident photon energy received by the ribbon structure(930). This framework operates on a pyroelectric effect to provide adetection structure for IR radiation.

FIG. 10 is a perspective view of a detector (1000) framework accordingto another exemplary embodiment of the invention, which is based on theVID concept. In general, the detector (100) comprises a substrate anddigital logic circuitry (not specifically shown, but similar to allembodiments discussed above) and a bridge structure formed on thesubstrate. The bridge structure includes a first support member (1010),a second support member (1012) and a ribbon structure (1030) suspendedbetween the support members (1010) and (1012) above the substrate. Thesupport members (1010) and (1012) are both insulating members.

In the exemplary embodiment of FIG. 10, the ribbon structure (1030)comprises an IR sensitive layer (1032) (pyroelectric layer), aninsulating layer (1034), a piezoelectric layer (1036) connecting members(1038) that provide electrical connections between layers (1032) and(1036), a second insulating layer (1037) and a resonator member (1039).The IR sensitive layer (1032) is made from a pyroelectric material thatgenerates a voltage from exposure to incident IR radiation. The voltagegenerated by layer (1032) is transferred to the piezoelectric layer(1036) via connections (1038), wherein the piezoelectric layer (1036)reacts to the voltage by creating stress as it tries to change itslength. This stress is transferred to the resonator (1039), which ismechanically coupled to the piezoelectric layer (1036) via the secondinsulating layer (1037). The stress imparted on the resonator layer(1039) by the piezoelectric layer (1036) causes the resonator member(1039) to change its resonant frequency in proportion to the amount ofincident IR exposure. The digital logic circuit coupled to the resonatormember (1039) (via the support members (1010, 10120 determines a changein the oscillating frequency of the resonator member (1039) due to forceexerted on the resonator member (1039) by the mechanical expansion andcontraction of the piezo layer (1036), wherein the change in frequencyis correlated to an amount of incident photon energy received by theribbon structure (1030). This framework operates on a pyroelectriceffect to provide a detection structure for IR radiation.

FIG. 11 is a perspective view of a detector (1100) framework accordingto another exemplary embodiment of the invention, which is based on theVID concept. In general, the detector (1100) comprises a substrate anddigital logic circuitry (not specifically shown, but similar to allembodiments discussed above) and a bridge structure formed on thesubstrate. The bridge structure includes a first support member (1110),a second support member (1120) and a ribbon structure (1130) suspendedbetween the support members (1110) and (1120) above the substrate. Aninsulating layer (1122) is interposed between the ribbon structure(1130) and the support member (1120).

The support member (1120) is a resonator member that operates at aresonant frequency and the support member (1110) is a fixed insulatingsupport structure. The ribbon structure (1130) comprises an IR sensitivelayer (1132), an insulating layer (1134), a piezoelectric layer (1136)and connecting members (1138) that provide electrical connectionsbetween layers (1132) and (1136). The IR sensitive layer (1132) is madefrom a pyroelectric material that generates a voltage from exposure toincident IR radiation. The voltage generated by layer (1132) istransferred to the piezoelectric layer (1136) via connections (1138),wherein the piezoelectric layer (1136) reacts to the voltage by creatingstress as it tries to change its length. This stress is transferred tothe resonator (1120), which causes it to change its resonant frequencyin proportion to the amount of incident IR exposure.

The framework and operation of the detector of FIG. 11 is similar tothat of FIG. 9, but where the ribbon structure (1130) of FIG. 11 isformed in an accordion or bellows shape. This shape increases thesurface area exposed to the incident photons. The increased area allowsfor more heating in the thermal IR mode and to generate more voltage inthe photoelectric mode, increasing the expansion characteristics.

FIG. 12 is a perspective view of a detector (1200) framework accordingto another exemplary embodiment of the invention, which is based on theVID concept. In general, the detector (1200) comprises a substrate anddigital logic circuitry (not specifically shown, but similar to allembodiments discussed above) and a bridge structure formed on thesubstrate. The bridge structure includes a first support member (1210),a second support member (1212) and a ribbon structure (1230) suspendedbetween the support members (1210) and (1212) above the substrate. Thesupport members (1210) and (1212) are both insulating members.

In the exemplary embodiment of FIG. 12, similar to the exemplaryembodiment of FIG. 10, the ribbon structure (1230) comprises an IRsensitive layer (1232) (pyroelectric layer), an insulating layer (1234),a piezoelectric layer (1236) connecting members (1238) that provideelectrical connections between layers (1232) and (1236), a secondinsulating layer (1237) and a resonator member (1239). The IR sensitivelayer (1232) is made from a pyroelectric material that generates avoltage from exposure to incident IR radiation. The voltage generated bylayer (1232) is transferred to the piezoelectric layer (1236) viaconnections (1238), wherein the piezoelectric layer (1236) reacts to thevoltage by creating stress as it tries to change its length. This stressis transferred to the resonator (1239), which is mechanically coupled tothe piezoelectric layer (1236) via the second insulating layer (1237).The stress imparted on the resonator layer (1239) by the piezoelectriclayer (1236) causes the resonator member (1239) to change its resonantfrequency in proportion to the amount of incident IR exposure.

The framework and operation of the detector structure of FIG. 12 issimilar to that of FIG. 10, but where the ribbon structure (1230) ofFIG. 12 is formed in an accordion or bellows shape. This shape increasesthe surface area exposed to the incident photons. The increased areaallows for more heating in the thermal IR mode and to generate morevoltage in the photoelectric mode, increasing the expansioncharacteristics.

FIG. 13 schematically illustrates a top view (10) and a side view (12)of an accordion or bellows shaped ribbon structure, wherein the ribbonis made of a single material. FIG. 14 schematically illustrates a topview (16) and a side view (14) of an accordion or bellows shaped ribbonstructure, wherein the ribbon is made of alternating materials A and B,which are different. The use of alternating materials on a photosensitive/IR sensitive ribbon layer (e.g., layers 1132, 1232) canprovide sensitivity with better linearity or wider or different spectralwavelengths. Moreover, the use of alternating materials on a resonatoror piezo ribbon layer (e.g., layered 1136, 1236, 1239) allows formaterials with different expansion coefficient characteristics tocontrol detector response, improve stress linearity, resonatorlinearity, or allow for custom response characteristics.

FIGS. 15A and 15B illustrate a photon detector (1500) according toanother exemplary embodiment of the invention, which is based on a CTEframework. FIG. 15A is a top view of the photon detector (1500) and FIG.15B is a cross-sectional view of the photon detector (1500) taken alongline 15B-15B in FIG. 15A. In general, as shown in FIGS. 15A and 15B, thephoton detector (1500) comprises a substrate (1502), a first supportmember (1510), a second support member (1520), fixedly connected to thesubstrate (1502), and a plate member (1530) disposed between the firstand second support members (1510) and (1520). In the exemplaryembodiment of FIG. 15, the first support member (1510) is a fixedinsulating support structure and the second support member (1520) is afixed resonator member that operates at a resonant frequency. The platemember (1530) is formed of one or more materials that are sensitive toIR energy, and having a thermal coefficient of expansion which causesthe plate member (1530) to expand and contract by absorption of incidentinfrared energy to exert force on the resonator support member (1520).

As further shown in FIGS. 15A and 15B, the first and second supportmembers (1510) and (1520) include grooves that insertably receiveopposing ends of the plate member (1530). The end portions of the platemember (1530) comprise supporting leg elements (1532) which serve tomaintain the IR absorbing portion of the plate member (1530) at someoffset height from the surface of the substrate (1502). This allows theplate member (1530) to be substantially thermally insulated from thesubstrate (1502).

In one embodiment, the plate member (1530) is disposed between the firstand second support members (1510) and (1520) in a “pre-stressed” state.In particular, in the “pre-stressed” state, the end portions of theplate member (1530) within the grooves of the first and second supportmembers (1510) and (1520) exert some minimal force against the innersurfaces of the first and second support members (1510) and (1520) inthe absence of any IR exposure. Indeed, pre-stressing the plate member(1530) between the first and second support members (1510) and (1520)serves many functions. For example, pre-stressing the end portions ofthe plate member (1530) against the inner side and top wall surfaces ofthe grooves prevents the plate member (1530) from moving out of positiondue to vibrations and camera movement. In addition, pre-stressing theplate member (1530) reduces or eliminates mechanical and vibrationnoise. Furthermore, pre-stressing the plate member (1530) against theresonator member (1520) eliminates fluctuations in data measurement dueto non-uniform stress distribution. Pre-stressing the plate member(1530) enables immediate readings of Δfo (change in oscillatingfrequency) of the resonator member (1520), which is cause by expansionof the plate member (1530) upon an increase in incident IR exposure onthe plate member (1530).

In some embodiments, disposing the plate member (1530) between the firstand second support members (1510) and (1520) in a “pre-stressed” statecan be realized by dimensioning the various support and plate elementsin a manner that the end portions of the plate member (1530) securelyfit (wedged) within the grooves of the support members (1510) and(1520). In other embodiments, a filler material may be used to fill anysmall gaps or spaces between the end portions of the plate member (1530)and the inner side and top wall surfaces of the grooves of the first andsecond support members (1510) and (1520). The filler material can be anysuitable material that will not cause the end portions of the platemember (1530) to adhere to the substrate (1502) or the first and secondsupport members (1510) and (1520), and which does not deteriorate due tothermal and mechanical conditions over repeated use and operation of thedetector (1500). For example, Teflon is one suitable material that canbe used for this purpose.

As in other embodiments, a digital logic circuit (not specificallyshown) is coupled to the resonator member (1520) for determining achange in the oscillating frequency of the resonator member (1520) dueto force exerted on the resonator member (1520) by the thermal expansionand contraction of the plate member (1530), wherein the change infrequency is correlated to an amount of incident infrared energyabsorbed by the plate member (1530).

It is to be understood that the specifications and material used forconstructing a detector (pixel) such as shown in FIGS. 15A/15B can varydepending on the application. For example, the substrate (1502) can bemade of materials such as silicon, glass, ceramic, etc. The size of eachdetector (pixel) can be about 40 um×45 μm, with a pixel pitch of about50 μm. The plate member (1530) can be made of materials or layers ofdifferent materials providing sufficient thermal expansion and thermalconductivity, such as Zn, Au, SiC (silicon carbide), ZnS (zincselenide), BN (boron nitride), ZnO (zinc oxide), or Si3N4 (siliconnitride), etc. The thermally conductive plate materials can befabricated to facilitate a larger direction of thermal conductivity in adirection beneficial to the design, wherein the larger conductivitydirection is parallel to the direction of the grain created by thefabrication. In other words, in the exemplary embodiment of FIGS. 15Aand 15B, the stress direction of the plate member (1530) can be in adirection along the substrate between the first and second supportmembers (1510) and (1520) as determined by the grain structure of theplate member (1530) created during fabrication.

In other embodiments, the plate member (1530) can be coated with anysuitable materials such as DLC, SiC, CaF2, etc., to enhance thermal IRabsorption in the 4 μm and 10 μm spectrum, for example. These coatingmaterials should have sufficient expansion and adhesive properties toprevent delamination over time. The resonator member (1520) may be madeof materials such as Lead Zirconate Titanate (PZT), Lead ScandiumTantalate, Barium Strontium Titanate, Bismuth Sodium Titanate (BNT),Barium Titanate (MHz range). The thermal and stress reaction timeconstants of the plate member (1530) should be made fast enough forstandard or faster video frame rates. For instance, a rise and fallcycle time of <2 ms would be sufficient for frame rates of 30 frames persecond.

FIGS. 16A and 16B illustrate a photon detector according to anotherexemplary embodiment of the invention, which is based on a CTEframework. FIG. 16A is a cross-sectional view of the photon detector(1600) taken along line 16A-16A in FIG. 16B, and FIG. 16B is a top viewof the photon detector (1600). In general, as shown in FIGS. 16A and16B, the photon detector (1600) comprises a substrate (1602), a firstsupport member (1610), a second support member (1620), a plate member(1630), and a resonator member (1640). The plate member (1630) isdisposed between the first support member (1610) and the resonatormember (1640). The first and second support members (1610) and (1620)are fixed insulating support structures. The resonator member (1640)operates at a resonant frequency. The plate member (1630) is formed ofone or more materials that are sensitive to IR energy, and having athermal coefficient of expansion which causes the plate member (1630) toexpand and contract by absorption of incident infrared energy to exertforce on the resonator member (1640).

As further shown in FIGS. 16A and 16B, the first support member (1610)comprises a slot (1612) formed in a sidewall thereof. The second supportmember (1620) is formed of two separate support elements, including afirst lower support element (1622) and a second upper support element(1624), which are fixedly disposed adjacent to, and in contact with, asidewall of the resonator member (1640). The lower and upper supportelements (1622) and (1624) are spaced apart to form a slot region (1626)there between. The plate member (1630) has one end inserted in the slot(1612) of the first support member (1610) and another end inserted inthe slot (1626) formed by the lower and upper support elements (1622)and (1624). The first and second support members (1610) and (1620)maintain the plate member (1630) at some offset height from the surfaceof the substrate (1602), such that the plate member (1630) is completelythermally insulated from the substrate (1602).

As in other embodiments discussed herein, a digital logic circuit (notspecifically shown) is coupled to the resonator member (1640) fordetermining a change in the oscillating frequency of the resonatormember (1640) due to force exerted on the resonator member (1640) by thethermal expansion and contraction of the plate member (1630), whereinthe change in frequency is correlated to an amount of incident infraredenergy absorbed by the plate member (1630).

Furthermore, it is to be understood that the specifications andmaterials that may be used for constructing a detector (pixel) such asshown in FIGS. 16A/16B can be those discussed above with reference toFIGS. 15A/15B. Moreover, in some embodiments, the plate member (1630)can be disposed between the first support member (1610) and theresonator member (1640) in a “pre-stressed” state, for reasons discussedabove. The various structures can be dimensioned such that the endportions of the plate member (1630) are securely fit (wedged) within theslots (1612) and (1626). In other embodiments, a filler material may beused to fill any small gaps or spaces between the end portions of theplate member (1630) and the inner surfaces of the slots (1612) and(1626) and the sidewall of the resonator member (1640).

FIGS. 17A and 17B illustrate a photon detector (1700) according toanother exemplary embodiment of the invention, which is based on a CTEframework. FIG. 17A is a cross-sectional view of the photon detector(1700) taken along line 17A-17A in FIG. 17B, and FIG. 17B is a top viewof the photon detector (1700) taken along line 17B-17B in FIG. 17A. Ingeneral, as shown in FIGS. 17A and 17B, the photon detector (1700)comprises a substrate (1702), a first support member (1710), a secondsupport member (1720) disposed the substrate (1702), and a plate member(1730). In this exemplary embodiment, the second support member (1720)is a rectangular-shaped resonator member having a cavity region (1722)formed in one surface thereof. An optional thin thermal insulating layer(not shown) may be disposed between the bottom surface of the resonatormember (1720) and the surface of the substrate (1702).

The plate member (1730) is disposed within the cavity region (1722) ofthe resonator member (1720). The plate member (1730) is secured in placein the cavity region (1722) by the first support member (1710). Thefirst support member (1710) may be a continuous rectangular framestructure that is fixedly secured to the top surface of the resonatormember (1720), wherein a portion of the first support member (1710)overlaps the inner sidewalls of the cavity region (1722) to provide alip that covers the upper peripheral surface edge of the plate member(1730), while leaving a large surface area for the plate member (1730)to absorb incident IR energy. In other embodiments, the first supportmember (1710) may comprise a plurality of separate elements that aredisposed in certain regions around the perimeter of the cavity region(1722) (e.g., each sidewall corner, or at a midpoint along eachsidewall, etc.) sufficient to maintain the plate member (1730) withinthe cavity region (1722).

In some embodiments, the plate member (1730) can be disposed within thecavity (1722) of the resonator member (1720) in a “pre-stressed” state,for reasons discussed above. The resonator member (1720) operates at aresonant frequency. The plate member (1730) is formed of one or morematerials that are sensitive to IR energy, and having a thermalcoefficient of expansion which causes the plate member (1730) to expandand contract by absorption of incident infrared energy to exert force onthe resonator member (1720). In the exemplary embodiment of FIGS.17A/17B, as the plate member (1730) expands in response to heatingcaused by absorption of incident infrared energy, the plate member(1730) exerts a force on the resonator member (1720) in threedimensions. In particular as shown in FIG. 17B, the plate member (1730)exerts a first horizontal force (Fx) in the x-direction on a first pairof opposing inner sidewalls of the cavity region (1720) of the resonatormember (1720), and a second horizontal force (Fy) in the y-direction ona second pair of opposing inner sidewalls of the cavity region (1722) ofthe resonator member (1720).

Moreover, as shown in FIG. 17A, the plate member (1730) exerts avertical force (Fz) against a bottom surface of the cavity region (1722)of the resonator member (1720) as the plate member (1730) expands in thez-direction between the overlapping lip portion of the first supportmember (1710) and the bottom surface of the cavity region (1722).Moreover, a vertical force Fz exerted against the bottom surface of thefirst support member elements (1710) will translate a vertical force tothe top surface of the resonator member (1720) along the sidewalls(which define the cavity region (1722)).

As in other embodiments discussed herein, a digital logic circuit (notspecifically shown) is coupled to the resonator member (1720) fordetermining a change in frequency of the resonant frequency of theresonator member (1720) due to force exerted on the resonator member(172) by the thermal expansion and contraction of the plate member(1720), wherein the change in frequency is correlated to an amount ofincident infrared energy absorbed by the plate member (1630). With theexemplary embodiment of FIGS. 17A/17B, the sensitivity of the detectoris increased as the change in frequency of the resonant frequency of theresonator member (1720) is due to stresses applied to the resonatormember (1720) in three (x-y-z) dimensions.

In all exemplary embodiments discussed above, the detector framework ispassive, i.e., the detector elements (e.g., CTE ribbons, CTE plates) arenot part of the active electrical circuit. When a device uses activepowered circuitry it is susceptible to electrical noise. This conceptwill be illustrated with reference to FIG. 18. FIG. 18 is a graphicalillustration (20) showing an advantage of using a direct-to-digitalpassive detector frameworks over conventional analog signal detector orquantum electronic designs, according to exemplary embodiments of theinvention. FIG. 18 illustrates electrical noise (26) that can mask orinterfere with an analog signal (22) containing desired sensor data,which is lost in noise (24). In order for the signal data to bedetected, it must be greater than noise level (or ‘noise floor’) (26).Any portion of the analog signal (24) below the ‘noise floor’ (26) islost information. The noise limits the sensitivity of the sensor systemto the level of the noise floor. Some systems go to great lengths toreduce the noise level to acquire better sensitivity. An example iscryogenic cooling. Although it achieves good sensitivity, it is complex,costly, cumbersome and dangerous.

One advantage of digital electronics is that data can be transmittedwith the greatest amount of immunity to noise as possible. An analogsignal (22) as shown in FIG. 18 is susceptible to noise because smallchanges in the signal data may be smaller in amplitude than the systemsnoise level or noise floor, which masks that part of the analog signal(so it is lost). This is a major limiting factor to any systems overallsensitivity and performance. In FIG. 18, the analog signal (22) can beconverted to a series of binary numbers (logic 1 and logic 0). Thesebinary numbers are represented by square waves (23) that modulatebetween the systems voltage low point and high point. To be detected,the square waves need only switch above or below the system transitionlevel (21) to be valid data. Digital design enable acquisition of validdata by using the leading or falling edge of the square wave signal.This trigger point is discernible even in high noise environments. So itis a clear advantage to have the systems data be digital at the earliestpossible time in the data creation scheme. In the exemplary detectorschemes discussed herein, a passive detector member is implemented, asit is more noise immune than active circuitry.

FIG. 19 is a block diagram of an imager system implementing passivedetectors, according to an exemplary embodiment of the invention. Ingeneral, FIG. 19 shows an imager circuit comprising a pixel structure(50), pixel circuitry (60), a read out integrated circuit (70) (“ROIC”),a controller (80), and an image rendering system (90). The pixel (50)comprises a passive detector front-end structure (52) and a resonatorstructure (54). The pixel circuitry (60) comprises a digital counter(62) and a tri-state register (64). The controller (80) comprises acounter enable/hold control block (81), a register reset block (82), anROIC control block (83), a data input control block (84), and a videooutput control block (85).

In the pixel structure (50) of FIG. 19, the passive detector front-endstructure (52) generically represents any one of the passive pixeldetector structures discussed herein, including the support structuresand detector elements (e.g., CTE ribbons, plates structures, etc.) thatare designed to be mechanically distorted in response to photonexposure, for example, and apply mechanical stress (force) to theresonator structure (54). The detector front-end structure (54) iselectrically passive and has no noise generating electronics.

The resonator structure (54) oscillates at a resonant frequency F_(o)and outputs a square wave signal. The resonator structure (54) isdesigned to have a reference (or base) resonant frequency (no photonexposure) in a state in which no additional stress, other than thepre-stress amount, is applied to the resonator structure (54) by thedetector front-end (52) due to photon exposure. As mechanical stress isapplied to the resonator member (54) from the detector front-end (52)due to photon exposure, the oscillating frequency of the resonatormember (54) will increase from its reference (base) resonant frequency.In one exemplary embodiment, the digital circuits (60), (70) and (80)collectively operate to determine the output frequency F_(o) of theresonator member (54) due to the force exerted on the resonator member(54) by the expansion and contraction of a passive detector element(e.g., ribbon, plate) of the detector front end structure (52),determine an amount of incident photonic energy absorbed by the passivedetector element based on the determined resonant frequency F_(o) of theresonator member (54) at a given time, and generate image data based onthe determined amount of incident photonic energy at the given time,which is then rendered by the imaging system (90).

In particular, the output signal generated by the resonator member (54)is a digital square wave signal having a frequency F_(o) that variesdepending on the stress applied to the resonator member (54) by thepassive detector front-end structure (52). The output signal generatedby the resonator member (54) is input to a clock input port of thedigital counter (62). For each read cycle (or frame) of the imager, thedigital counter (62) counts the pulses of the output signal from theresonator member (54) for a given “counting period” (or referenceperiod) of the read cycle. The counting operation of the digital counter(62) is controlled by a CLK enable signal generated by the countercontrol block (81) of the controller (80). For each read cycle, thecount information generated by the counter (62) is output as an n-bitcount value to the tri-state register (64).

The ROIC 70 reads out the count value (pixel data) from the pixelcircuitry (60) of a given pixel (50) for each read cycle. It is to beunderstood that for ease of illustration, FIG. 19 shows one pixel unit(50) and one corresponding pixel circuit (60), but an imager can have aplurality of pixel units (50) and corresponding pixel circuits (60)forming a linear pixel array or a 2D focal plane pixel array, forexample. In this regard, the ROIC (70) is connected to each pixelcircuit (60) over a shared n-bit data bus (66), for controllablytransferring the individual pixel data from the each pixel countingcircuit (60) (which is preferably formed in the active silicon substratesurface under each corresponding pixel structure (50)) to the controller(80).

In particular, in response to control signals received from the ROICcontrol block (83) of the controller (80), the ROIC (70) will output atri-state control signal to the pixel circuitry (60) of a given pixel(50) to read out the stored count data in the shift-register (64) ontothe shared data bus (66). The shift-register (64) of each pixel circuit(60) is individually controlled by the ROIC (70) to obtain the countdata for each pixel at a time over the data bus (66). The count data istransferred from the ROIC (70) to the controller (80) over a dedicateddata bus (72) connected to the n-bit data input control block (84) ofthe controller (80). After each read cycle, the tri-state register (64)of each pixel will be reset via a control signal output from theregister reset control block (82) of the controller (80).

The controller (80) processes the count data obtained from each pixel ineach read cycle (or video frame) to determine the amount of incidentphoton exposure for each pixel and uses the determined exposure data tocreate a video image. The video data is output to an image renderingsystem (90) via the video output block (85) to display an image. In someembodiments of the invention where the counter (62) for a given pixel(50) obtains count data for the given pixel (50) by directly countingthe output frequency generated by the resonator member (54), thecontroller (80) will use the count data to determine a grayscale levelfor the pixel, which corresponds to the amount of the incident photonicexposure of the pixel. For example, in some embodiments, the grayscalelevel can be determined using a grayscale algorithm or using a lookuptable in which the different grayscale values (over a range from blackto white) are correlated with a range of count values for a prioridetermined increments of changes in the oscillating frequency of theresonator member from the base reference frequency to a maximumoscillating frequency. The maximum oscillating frequency is the highestfrequency that can output from the resonator member in response to themaximum amount of stress force that can be created by the given passivedetector front-end structure.

In other embodiments of the invention, the pixel structure and pixelcircuitry of FIG. 19 can be modified such that the counter will countthe frequency of a signal that represents the difference between thebase resonant frequency of the resonator member (54) and the actualoutput frequency generated by the resonator member (54) at a given timein response to stress applied by the passive detector front-end (52).For example, FIG. 20 illustrates another exemplary embodiment of a pixelunit and pixel circuitry that can be implemented in the imager system ofFIG. 19. In FIG. 20, the pixel (50) (of FIG. 19) is modified to includea reference oscillator (56) that outputs a reference resonant frequencyF_(ref). The pixel circuitry (60) (of FIG. 19) is modified to include anexclusive-Or gate (66) that receives as input, the output signal of theresonator member (54) (having a variable frequency Fo) and the fixedsignal from the reference oscillator (56). The X-Or gate (66) operatesto remove the base frequency component of the signal F_(o) output fromthe resonator member (54) based on the reference frequency of thereference oscillator (56) and outputs a square wave signal having afrequency equal to the change ΔF_(o) in frequency of resonator member(54). The ΔF_(o) frequency signal, which is much lower in frequency thanthe oscillating frequency Fo of the resonator member (54), requires alower bit number counter (62) to count the ΔF_(o) signal, making itsimpler to implement. As with the embodiments of FIG. 19, the ΔF_(o)signal is counted for a reference period and the count value is used todetermine incident photon exposure of the pixel, as discussed above.

Although exemplary embodiments have been described herein with referenceto the accompanying drawings for purposes of illustration, it is to beunderstood that the present invention is not limited to those preciseembodiments, and that various other changes and modifications may beaffected herein by one skilled in the art without departing from thescope of the invention.

What is claimed is:
 1. A device, comprising: a substrate; a photondetector formed on the substrate, wherein the photon detector comprises:a piezoelectric resonator configured to generate an output signal havinga frequency or period of oscillation; an unpowered detector, wherein theunpowered detector is configured for photon exposure, wherein theunpowered detector comprises a material having a thermal coefficient ofexpansion that causes the unpowered detector to distort due to saidphoton exposure, wherein the unpowered detector is further configured toapply a mechanical force to the piezoelectric resonator due to saiddistortion of the unpowered detector, and cause a change in thefrequency or period of oscillation of the output signal generated by thepiezoelectric resonator due to said mechanical force applied to thepiezoelectric resonator; and digital circuitry configured to (i)determine the frequency or period of oscillation of the output signalgenerated by the piezoelectric resonator as a result of the mechanicalforce applied to the piezoelectric resonator by the unpowered detector,and to (ii) determine an amount of said photon exposure based on thedetermined frequency or period of oscillation of the output signalgenerated by the piezoelectric resonator.
 2. The device of claim 1,wherein the photon detector is configured to detect thermal infraredenergy having a wavelength in a range of about 2 micrometers to 25micrometers.
 3. The device of claim 1, wherein the photon detectorfurther comprises a first support, wherein the unpowered detectorcomprises a ribbon, and wherein the ribbon is suspended above saidsubstrate and supported by the first support and the piezoelectricresonator, wherein the ribbon comprises a material having a thermalcoefficient of expansion, which causes the ribbon to distort due to saidphoton exposure and apply said mechanical force to the piezoelectricresonator.
 4. The device of claim 3, wherein the first support iscomprises a fixed insulating support.
 5. The device of claim 3, whereinthe photon detector further comprises a reflector disposed on thesubstrate beneath the ribbon.
 6. The device of claim 1, wherein thephoton detector further comprises a first support, wherein the unpowereddetector comprises a plate, and wherein the plate is disposed betweenthe first support and the piezoelectric resonator, wherein the platecomprises a material having a thermal coefficient of expansion, whichcauses the plate to distort due to said photon exposure and apply saidmechanical force to the piezoelectric resonator.
 7. The device of claim6, wherein the first support has a first groove and wherein thepiezoelectric resonator comprises a second groove, wherein ends of theplate are disposed within the first and second grooves.
 8. The device ofclaim 6, wherein the photon detector further comprises a second support,disposed adjacent the piezoelectric resonator, wherein the first supporthas a first groove and wherein the second support comprises a secondgroove, wherein ends of the plate are disposed within the first andsecond grooves, wherein the second groove allows the plate to apply saidmechanical force to the piezoelectric resonator as the plate distortsdue to said photon exposure.
 9. The device of claim 6, wherein the plateis disposed between the first support and the piezoelectric resonator ina pre-stressed state.
 10. The device of claim 1, wherein thepiezoelectric resonator comprises a recessed cavity region formed in asurface of the piezoelectric resonator, wherein the unpowered detectorcomprises a plate that is disposed within the recessed cavity region ofthe piezoelectric resonator, wherein the photon detector furthercomprises a first support that is disposed on the surface of thepiezoelectric resonator and overlapping at least a portion of therecessed cavity region to secure the plate within the cavity region, andwherein the plate comprises a material having a thermal coefficient ofexpansion, which causes the plate to distort due to said photon exposureand apply said mechanical force to the piezoelectric resonator.
 11. Thedevice of claim 10, wherein the first support comprises a continuousframe structure that is fixedly secured to the surface of thepiezoelectric resonator, wherein a portion of the first support overlapsthe inner sidewalls of the cavity region to provide a lip that coversthe upper peripheral surface edge of the plate, while leaving an opensurface area for the plate for said photon exposure.
 12. The device ofclaim 10, wherein distortion of the plate causes said mechanical forceto be applied to the piezoelectric resonator in three dimensions. 13.The device of claim 10, wherein the plate is disposed within therecessed cavity of the piezoelectric resonator in a pre-stressed state.14. A thermal imaging system comprising the device of claim
 1. 15. Amethod, comprising: exposing a photon detector to incident photons,wherein the photon detector comprises an unpowered detector, and apiezoelectric resonator, wherein the piezoelectric resonator isconfigured to generate an output signal having a frequency or period ofoscillation; distorting the unpowered detector due to said photonexposure, wherein the unpowered detector comprises a material having athermal coefficient of expansion that causes the unpowered detector todistort due to said photon exposure; applying a mechanical force to thepiezoelectric resonator due to the distorting of the unpowered detector;determining a frequency or period of oscillation of the output signalgenerated by the piezoelectric resonator as a result of the mechanicalforce applied to the piezoelectric resonator by the unpowered detector;and determining an amount of said photon exposure of said photondetector based on said determined frequency or period of oscillation ofthe output signal generated by the piezoelectric resonator.
 16. Themethod of claim 15, further comprising generating image data using thedetermined frequency.
 17. The method of claim 15, wherein determining anamount of said photon exposure comprises: generating count data bycounting a number of digital pulses in the output signal generated bythe piezoelectric resonator for a given counting period; and determininga level of photon exposure based on said count data.
 18. A device,comprising: a substrate; a photon detector formed on the substrate,wherein the photon detector comprises: a first electrode and a secondelectrode; a piezoelectric resonator configured to generate an outputsignal having a frequency or period of oscillation, wherein thepiezoelectric resonator is connected to the first and second electrodesand suspended above a surface of the substrate, wherein the first andsecond electrodes apply a drive voltage to the piezoelectric resonator;an unpowered detector, wherein the unpowered detector is mechanicallycoupled to the piezoelectric resonator, wherein the unpowered detectoris configured for photon exposure, wherein the unpowered detectorcomprises a material having a thermal coefficient of expansion thatcauses the unpowered detector to distort due to said photon exposure,wherein the unpowered detector is further configured to apply amechanical force to the piezoelectric resonator due to said distortionof the unpowered detector, and cause a change in the frequency or periodof oscillation of the output signal generated by the piezoelectricresonator due to said mechanical force applied to the piezoelectricresonator; and digital circuitry configured to (i) determine thefrequency or period of oscillation of the output signal generated by thepiezoelectric resonator as a result of the mechanical force applied tothe piezoelectric resonator by the unpowered detector, and to (ii)determine an amount of said photon exposure based on the determinedfrequency or period of oscillation of the output signal generated by thepiezoelectric resonator.
 19. The device of claim 18, wherein the photondetector further comprises a fixed support connected to the substrate,wherein end portions of the unpowered detector are mechanically coupledto the fixed support and the piezoelectric resonator.